The present invention relates to a multi-stage arsenic doping process to achieve low resistivity in silicon crystal grown by Czochralski method.
Arsenic is an ideal dopant used to achieve lower resistivity in silicon crystals grown by Czochralski process because of its high solubility in silicon. However arsenic is highly volatiles at temperature higher than 617.degree. C. The Surface of the silicon melt: is at its melting point (1412.degree. C.) or higher. In popular practice, arsenic is fed into the melt from a feed hopper located a few feet. above the melt level. However, due to higher temperatures, loss of arsenic to surrounding environment (argon gas) is violent, which results in generation of particles. Generation of oxide- particles (sub-oxides) is enhanced by local reduction in temperature caused by sublimation of arsenic. These particles can act as heterogeneous nucleation sites and often result in failure of the crystal pulling process. Excessive generation of particles does not allow sufficient doping of arsenic to achieve higher arsenic concentrations in the melt required to achieve lower resistivity targets.